This invention relates to a method for driving and controlling liquid crystal which stepwise controls a liquid crystal shutter array to record images on a photosensitive material at half tone and to a device therefor.
FIG. 1 is a schematic view of an image recording device using a liquid crystal shutter array to which this invention is applicable wherein light emitted from a light source 1 such as a Halogen lamp is directed onto a liquid crystal shutter array 2 comprising a number of liquid crystal cells 2A of a rectangular shape arranged in line, the light transmitted through opened liquid crystal cells 2A is irradiated onto a photosensitive material 3 via filter unit 10 to expose the photosensitive material 3 at a recording area 3A linearly extending in the width of .DELTA.D. After one line is recorded, the photosensitive material 3 is operatively moved in the direction Q by .DELTA.D to record another data in the next line in a manner similar to the above.
The filter unit 10 includes a cylindrical filter plate 12 and a Selfoc lens array 11 which is internally held at a center of the cylindrical filter plate 12. FIG. 2 shows the filter unit 10 in brief cross section. The cylindrical filter plate 12 comprises mask members 12M1, 12M2 of a band shape which are arranged symmetrically from a central point to block the light transmitted from the liquid crystal shutter array 2, and band-shaped red filters 12R1, 12R2, green filters 12G1, 12G2 and blue filters 12B1, 12B2 which are respectively arranged symmetrically from the center in the order of red (R), green (G) and blue (B) from the mask members 12M1, 12M2. The Selfoc lens array 11 is fixed inside the cylindrical filter plate 12 in a manner to allow rotation in the direction of, for instance, P around the longitudinal axis of the cylinder. Since the cylinder rotates in the direction P. the light coming through the liquid crystal shutter array 2 is either blocked out by the mask members 12M1 and 12M2 or allowed to pass the R light through the red filters 12R1 and 12R2, the G light through the green filters 12G1 and 12G2 of the B light through the blue filters 12B1 and 12B2. By rotating the cylindrical filter plate 12 suitably, the recording area 3A extending in a linear form on the photosensitive material 3 is consecutively exposed to the R light, G light and B light or is blocked of the light by the mask members 12M1 and 12M2. After one line of recording area on the photosensitive material 3 is exposed to the lights R, G and B, the photosensitive material 3 is moved in the direction Q to expose the next one line of the recording area to the light so that color images on the photosensitive material 3 is completed by repeating the above recording operation one line by one line.
The liquid crystal cells 2A of the liquid crystal shutter array 2 have such features that they are closed to prohibit passing of the light therethrough (in other words, the intensity of the light transmitted is zero) when a pulse voltage PV (e.g. 1 KHz) is applied to the liquid crystal cells 2A, while they are open to let the light pass therethrough when no pulse voltage is applied thereto. FIG. 3 shows that a liquid crystal shutter is closed until a time point t.sub.o while it is open between a time point t.sub.o and a time point t.sub.4 to let the light pass therethrough. The graph also indicates that while the intensity of the transmitted light increases gradually (the small dip in the curve is indicative of the well known bound phenomenon of the liquid crystal); when the liquid crystal shutter starts to let the light pass, the passage of light instantaneously shut when a pulse voltage PV is applied at the time point t.sub.4 and the shutter closes (CL). The intensity of the light which passes through the liquid crystal shutter array 2 to expose the photosensitive material 3 can be controlled by the steps of keeping the pulse voltage PV applied on the liquid crystal cells 2A at zero to open the liquid crystal shutter, keeping the pulse voltage PV at zero at different time points, for example t.sub.1, t.sub.2, t.sub.3, and thereby controlling the time OP during which the liquid crystal shutter is open. In other words, the amount of light which exposes the photosensitive material 3 can be controlled so that the color images can be recorded on the photosensitive material 3 at half tone.
Optimally toned images can be recorded by controlling the time period OP during which the liquid crystal shutter is open, or more specifically by applying gradation density signals as shown in FIG. 4 to the liquid crystal shutter array 2. If it is assumed that the liquid crystal cells 2A of the liquid crystal shutter array 2 comprises N number of cells 21, 22, . . . , 2 (N-1), 2N, the time during which the liquid crystal cells 21 through 2N are open can be controlled by simply applying the gradation density signals shown in schema (A) of FIG. 4 to each of the liquid crystal cells. FIG. 4 shows an example wherein the images are recorded at the gradation density of 4 bits in the level "0" to "15". The liquid crystal cell 21 opens for "0", if expressed in terms of the gradation density, and the liquid crystal cell 22 opens for "1". Similarly, the liquid crystal cell 2N opens for "4". By applying the pulse voltage signals on the liquid crystal cells 21 through 2N at timings corresponding to the gradation densities as shown in schema (A) of FIG. 4, the time to open the respective liquid crystal cells 2A can be controlled. Since the photosensitive material 3 is exposed with the light transmitted through the liquid crystal cells 21 through 2N, the photosensitive material 3 can be recorded with the images at an optimally adjusted gradation tone.
FIG. 5 shows a conventional circuit which may be used as a control circuit for recording images at adjusted gradation tone by using the liquid crystal shutter array 2 described above. If the number of the liquid crystal cells 21 through 2N of the shutter array 2 is N, and the number of gradients in output images is n bits, image data PD is stored in a line memory 100 having N.times.n bits. The data prepared in correspondence with all the liquid crystal cells 21 through 2N (#1 through #N) in the line memory 100 are respectively transmitted to shift registers 111 through 11N, and the output data therefrom are latched respectively in latch circuits 121 through 12N in synchronism with a latch pulse LP. Selectors 131 through 13N are provided in correspondence to the respective liquid crystal cells 21 through 2N and are supplied respectively with pulse width signals PW signals of the pulse width corresponding to the data (gradation signals) which have been latched in the latch circuits 121 through 12N are operatively selected by the selectors 131 through 13N and fed to a liquid crystal driver 101. The liquid crystal driver 101 then sends the pulse width signals SW selected by the selector 131 through 13N to the liquid crystal cells 21 through 2N of the liquid crystal shutter array 2. Thus, each of the liquid crystal cells 21 through 2N of the shutter array 2 is respectively supplied with signals of the time widths PD1, PD2, PD3, . . . , PDN corresponding to the gradation densities as shown in the schema (A) of FIG. 4.
The prior art liquid crystal driving control circuit, however, is detrimental as it requires shift registers 110 (111 to 11N), the latch circuits 120 (121 to 12N) and the selectors 130 (131 to 13N) in the number corresponding to the number of the liquid crystal cells 21 through 2N of the liquid crystal shutter array 2 to inevitably complicate the circuit and push up the production cost.